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What Does Fill Power Mean?

by Stefan Hunter

If you have ever shopped for bedding, outerwear, or sleeping bags, you may have come across the term 'fill power'. But what exactly does it mean? Fill power can be defined as simply 'how fluffy down is'. Technically speaking, it is measured using a specially calibrated measurement system; but for most consumers, 'high fill power equals fluffy'. So why does fill power matter, and when does it make sense to spend more on a high fill power item?

Fill power is only used to describe the loftiness of down, not feathers. Fill power also only applies to down and not down
alternatives, although occasionally it is used as a reference, for example, '550 fill power down' (DOWNLITE sometimes will use this as a reference for our down alternatives, such as PrimaLoft).

The actual measurement of fill power involves placing 1 ounce of treated down into a specially designed filling tube. Next a calibrated weight is added on top and allowed to push against the down for a set period of time (24 hours as a baseline). Elements like temperature and humidity can alter the results, so the down is tested in a controlled environment.

For bedding like comforters, blankets, and throws, having a high fill power means that the article of bedding can keep you warmer, but with less weight. For other items like pillows, it is not as important to have a high fill power number because you're resting your head weight against the item. A high fill power does give you a nice 'bounce' in terms of how a pillow springs back against your weight; a result which some sleepers prefer. Other sleepers, like more of the 'cradle' effect and a basic fill power of 550 feels great and fits their budget.

Generally, the higher the fill power, the higher the cost of the material. In fact, the price curve is less linear in shape, and tends to be more exponential. So if you're buying a new comforter and you want that cloud like feeling on top of you, opt for a high fill power in the 700-800 range.

Other things to consider for fill power, is the material in which it is placed or stored. When high fill power is sought, it is preferred to compliment it with a very light weight fabric weave that is a paper thin fabric that is extremely light weight, yet down proof.

It can be a little confusing for consumers to understand how fill power and weight can impact the warmth of an item, as well as comparing 'like' items at a store. If two comforters have the same fill power, then the only difference that can impact warmth between the two is the physical weight used for its filling. A typical heavy winter comforter might be in the 60 oz. range using a 600 fill power white goose down. However, the same fill power but at a lighter weight 48 oz., can make the item offer less warmth.

They way down works is by providing a barrier to store your own body's warmth. So the high fill power down basically holds that warm ambient air in place, thus letting you stay snuggly warm.

A common mistake made by consumers is to overbuy the fill power or warmth of a comforter, which results in an unpleasant 'too warm' sleep environment. For first time buyers we always suggest a lower warmth level to make sure you don't get too warm. Consumers with previous down experience can then opt for higher fill power comforters, knowing how the materials work to provide their desired warmth and comfort.